The two were to appear for preliminary hearings in the afternoon. Prosecutors were seeking $1 million bail at the first hearing on a charge of attempted murder.
Police said all three girls were at a sleepover Friday night. The two suspects allegedly lured the third girl into a wooded area Saturday and stabbed her 19 times.
A cyclist found the victim, who had crawled out of the woods, by a roadside. She was reported to be in stable condition Monday, but police said her injuries could still be life-threatening.
The two suspects were arrested Saturday afternoon after a Waukesha County deputy found them walking near Interstate 94.
Investigators said the two girls had become fascinated by a website featuring stories about violence and death. They were also fans of a female character appearing on several websites.
"As the details became more apparent, it's extremely disturbing as a parent and as a chief of police, especially with the age of the suspects and being female" Police Chief Russell Jack said. "This is a very disturbing investigation. "The Internet can be full of dark and wicked things. Unmonitored and unrestricted access to the Internet by children is a growing and alarming problem."
Jack said police were withholding the names of all three girls and releasing little information about the website that might have inspired the attack.